Process Control for Solder Flux
Flux used in ball grid array (BGA) and chip scale package (CSP) manufacturing has been increasing in importance with requirements to hold smaller solder balls in place, adequately clean solder surfaces, and leave no residues. It is known in the packaging industry that insufficient or excess flux can cause a variety of defects however, a non-destructive process control tool capable of properly setting up and monitoring production parameters for flux dispense has not been available. It is difficult to measure a non-Newtonian, temperature sensitive, transparent, viscous fluid in-situ. Crude sampling measurements based on microscopes or weighing scales are in use on the manufacturing floor. This paper reviews a new technique called "fluorescence intensity mapping" which accurately measures flux location, height and volume of flux deposits.
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